The present invention relates to apparatus for use in driving tunnels, galleries, adits, roadways and similar underground excavations referred to hereinafter simply as "tunnels".
It is known to produce a tunnel with apparatus employing a front shield which protects local equipment at the working face. The shield may be a continuous cylindrical component or a knife or drive shield composed of elongate drive members supported for displacement on a frame. Normally the shield contains such equipment as cutting appliances or devices or maybe a drifting machine and/or conveyor means for removing material detached from the working face. Where a knife or drive shield is utilized the drive members are thrust forward to penetrate the working face with the aid of hydraulic rams which advance the drive members individually or in groups. When the drive members have all been advanced the frame is drawn up by operating all the rams in unison.
In tunnel driving processes performed with apparatus as aforesaid there is often a tendency for the front shield to roll or turn about the longitudinal central axis of the apparatus and this can cause serious problems. In order to correct such a tendency and primarily to stabilize a drive or knife shield it is known from U.S. Pat. No. 4,012,916 to provide a drifting cutter which can be advanced independently to cut a channel in the floor of the tunnel. The advanced cutter then inhibits the drive shield from rotating about its axis. The drifting cutter can also be positionally displaced to enable enhanced control and guidance of the drive shield. Where the front shield is of the cylindrical type then it is known from Swiss patent No. 453 414 to provide a pressure ring inside the shield and to couple the shifting rams between the shield and the pressure ring in a flexible manner. The pressure ring is itself rotatable about its central axis by means of additional hydraulic units which can impart pre-loading torque to the pressure ring. This pre-loading torque is then transferred through the shifting rams to the main shield to compensate for any turning motion therein. It is also known from German patent No. 2 621 421 to utilize a support affixed to a follow-up rear shield which engages with guide on the front shield. The support and the guide can take up offset positions so that as the front shield is advanced it tends to turn to compensate for turning movement in the opposite direction.
A general object of the present invention is to provide an improved form of apparatus.